1. Field of the Invention
This invention relates to motion picture systems, and more particularly to a shutter drive control circuit. The circuit enables the system to make a motion picture of uniform quality to the last frame of a sequence for each cycle of actuation followed by release of a shutter trigger however long the exposure time selected.
2. Description of the Prior Art
Motion picture cameras are generally provided with a rotary shutter having a cutout at an open angle of about 150.degree. and which is driven for continuous rotation at a selectively controlled speed corresponding either to 18 frames/sec. for normal operation (in the case of 8 m/m cameras), or to 9 frames/sec., or to 24 or 25 frames/sec. for slow motion reproduction. To effect uniformity in quality of the motion picture taken with different frame speed, it is necessary to control the size of opening of a diaphragm aperture in accordance not only with the preselected frame speed or exposure time but also with the sensitivity of the film used and the level of brightness of a scene being photographed.
With such a motion picture camera it may be impossible to derive proper exposures for all photographic situations which may be encountered because the required diaphragm aperture may not be available in for a low light level. Attempts have been made to extend the dynamic range of the camera toward low light levels by increasing the angle of an opening of the shutter up to 220.degree. for example. A further large increase of the opening angle can not be realized because of the lack of design flexibility in the shutter structure itself and because of the difficulty of establishing an effective cooperation between a shutter mechanism and an intermittent film advancing mechanism. For these reasons, the dynamic range of exposure control for a motion picture camera is not as extensive as desired.
It is known to provide a motion picture system employing a one-shot control circuit with magnetic means which enables the shutter to be stopped for each initiation of a frame exposure and to remain stationary for a predetermined time interval and then to be driven for further rotation at the termination of duration of the predetermined time interval. In this conventional type of motion picture system, initiation of driving of the shutter is controlled directly by actuation and release of a shutter trigger, and the operator releases the shutter trigger in order to terminate a continuous series of frame exposures. However when the release of the trigger coincides with the making of the last frame of that series, no correct exposure can be made for the last frame.